These are impregnable fortresses of the Turks located at the top of the hill of Bizani.
They were built under the supervision of the German general Goltz (VON DER GOLTZ) during the years 1909-1912 but also during the war. Apparently the Turks were expecting this war and had taken action. The material from which the forts are made is reinforced concrete. They are built in a semicircular orbit.
Thus, they are invisible from the side they are supposed to be attacked, except for the muzzle of the cannons that was visible. The shooter is covered and only when he is going to aim he pulls out his head. The forts are directed and have cannons facing south, because from there they expect an attack but some of them face to the east.